China Library ClassificationNo.: TP274 Document IdentificationNo.: A.
Application of PLC in elevator control system
Xiang Jing mei
(Beijing Beike Masi Automation Engineering Co., Ltd., Beijing 102200, China)
This paper introduces the elevator control based on PLC. The displacement feedback of the rotary encoder is realized by PLC, and the flow counting, call speed change and timing signal are realized by PLC program, which replaces the reliability and arrival accuracy of the position detection device of the system.
Keywords: elevator; PLC displacement control; speed control
1 Introduction
With the continuous development of urban construction, there are more and more high-rise buildings. As a vertical transportation tool in high-rise buildings, elevators have been inseparable from people's daily life. At present, elevator control generally adopts two ways. One is to use microcomputer as signal control unit to complete the collection of elevator signals, the setting of operation state and function, and realize the automatic dispatching and centralized operation of elevators, and the traction control is completed by frequency converter; The second control mode uses programmable controller instead of microcomputer to realize signal control. There is not much difference between the two methods in control mode and performance. PLC has high reliability and convenient and flexible program design. On the basis of realizing the double closed loop of current and speed by using PLC to control frequency conversion and speed regulation, this design realizes the three-loop control of current, speed and displacement without increasing hardware equipment.
2 hardware circuit
2. 1 hardware structure
The hardware structure diagram of the system is shown in figure 1.
PLC is Siemens S7-200 series CPU22 1. PLC receives the call signals from the control panel and the call boxes on each floor, the function signals of the car and door system, and the status signals of the hoistway and frequency converter, and realizes the centralized selection control of the elevator through program judgment and operation. While outputting display and monitoring signals, PLC sends signals such as running direction, startup, acceleration and deceleration operation, elevator braking, etc. to the frequency converter.
2.2 Current and speed double closed-loop circuit
VS-6 16G5 CIM- RG5A 4022 inverter of YASAKWA company is adopted. The frequency converter itself has a current detection device to form a current closed loop; Two-phase pulses A and B are generated by a rotary encoder coaxially connected with the motor and enter the frequency converter, and a speed closed loop is formed by pulse counting while confirming the direction.
3 displacement and running curve control
As a manned tool, elevator requires not only safety and reliability, but also stable operation, comfortable ride, accurate parking and ideal displacement control of 3. 1 running curve under potential load.
Double-loop control of variable frequency speed regulation can basically meet the requirements, but it needs to be further improved compared with foreign high-performance elevators. This design is based on this idea. At the same time, the existing rotary encoder is used to form a speed loop. At the same time, the PG card of the inverter outputs the number of pulses proportional to the motor speed and elevator displacement, which is introduced into the high-speed counting input port 0000 of PLC. By accumulating the number of pulses, the pulse equivalent is calculated by formula (1), and the elevator position is determined.
Elevator displacement h=SI
Where I: cumulative pulse number S: pulse equivalent.
S=lpD/(pr) ( 1)
The reduction ratio of the reducer used in this system is 1 = 1/20, which produces traction.
Wheel diameter D=580mm, rated motor speed ne = 1 450r/min, corresponding to the number of pulses per revolution of rotary encoder p= 1024, and frequency division ratio of PG card r =118, which is equivalent to (1.
S = 1.6 mm/pulse
3.2 Speed control
This method is realized by using D/A module of PLC extended function module. The digitized ideal speed curve is pre-stored in the PLC register. When the program is running, the D/A is written by looking up the table, and the D/A is converted into simulation and then the ideal curve is output.
3.2. 1 Accelerate the generation of a given curve.
The 8-bit D/A output is 0 ~ 5v/0 ~ 10v, and the corresponding digital value is16,00 ~ ff, ***255 level. It takes 2.5 ~ 3 seconds to accelerate the practice of Toyo elevator. According to the conservative value, the time interval of checking the table every time the elevator accelerates should not exceed10 ms.
Because the elevator logic control part has the largest program, and the PLC operation adopts the periodic scanning mechanism and the usual table lookup method, the instruction time interval of each table lookup is too long, which can not meet the accuracy requirements of a given curve. During the operation of PLC, the information exchange between CPU and various devices, the execution of user programs, signal acquisition and the output of control variables are all carried out in a fixed order in the form of circular scanning, and all functions should be queried, judged and operated in each cycle. This order and format cannot be changed artificially. Usually, in a scanning cycle, six steps are basically completed, including running monitoring, exchanging information with programmers, exchanging information with digital processors, exchanging information with communication processors, executing user programs and I/O interface services. In a cycle, the CPU only executes the whole user program once. This mechanism has its convenience, but its real-time performance is poor. The long scanning time directly affects the response effect of the system to the signal. On the premise of ensuring the control function, it is a very complicated problem to minimize the periodic scanning time of CPU. Generally speaking, this method can only proceed from the shortest execution time of the user program. The program scanning time of elevator logic control part has exceeded10 ms. Although some measures have been taken to reduce the program scanning time, it is still impossible to reduce the scanning time below10 ms. At the same time, the braking curve adopts the distance principle, and the response time of each distance should not exceed10 ms. In order to meet the real-time requirements of the system, this paper adopts the interruption method in the generation of speed curve.
The PLC used in this paper has three interrupt functions: (1) external interrupt; (2) High-speed counting of internal interrupts (3) Periodic interrupts. The first two interrupts each have 8 breakpoints, and the latter has 4 breakpoints. The latter two interrupt modes are adopted in the program. The start-up process adopts fixed-period interrupt, and the braking process adopts high-speed counting internal interrupt. After the interrupt service program is put into the main program, the logic control such as running state detection, running protection, internal selection and external call are all realized in the main program. Programs related to the generation of operation curves, such as the judgment of operation conditions, the selection of operation modes, and table lookup, are all placed in the interrupt service program.
Starting the acceleration operation is completed by the periodic interrupt service program. This interrupt cannot be switched by the program. Once set, it will be interrupted periodically at a set time interval. Therefore, the starting operation conditions should be placed in the interrupt service program. When the operation conditions are not met, the interrupt will return.
3.2.2 Generation of deceleration braking curve
In order to ensure the completion of the braking process, it is necessary to judge the braking conditions and determine the deceleration point in the main program. Before the deceleration point is determined, the elevator is always in the process of acceleration or steady speed operation. The acceleration process is completed by a fixed interruption time. After the acceleration reaches the maximum value of the corresponding mode, the running conditions of the acceleration program are no longer satisfied. After each interruption, the acceleration program will not be executed and will return directly from the interruption. The elevator runs at the maximum value of the corresponding mode, and after the deceleration point of this mode, a high-speed counting interrupt is generated, and the deceleration service program is executed. In this interrupt service program, modify the conditions of the counter setting value to ensure the execution of the next interrupt.
In the internal register of PLC, the values of the deceleration curve table are arranged from big to small, and the table pointer is added with 1 every interruption, so the look-up table value of the next interruption will be smaller than that of this interruption. The judgment of door area and floor area is given by external signals to ensure the reliability of deceleration process.
4 programming
The pulse signal is introduced into the high-speed counting input of PLC by using the PG card output of frequency converter to form position feedback. The number of pulses accumulated by the high-speed counter reflects the position of the elevator. The value of the high-speed counter is constantly compared with the number of pulses corresponding to each signal point, so as to judge the running distance, speed change point, leveling point and braking stop point of the elevator. Theoretically, the leveling error of this control method can be within a pulse equivalent range. Considering the mechanical factors such as gear clearance of reducer, the leveling accuracy of elevator can reach, far below the national standard, and meet the requirements of smooth braking, smooth operation and accurate leveling. In the process of elevator operation, the software calculates the following position signals in real time through position signal detection: elevator floor position, fast speed change point, medium speed change point, door area signal and flat floor position signal. The following introduces five subprograms: floor counting, fast speed change, medium speed change, door area and floor signal, which are added on the basis of centralized selection control.
4. 1 number of floors
This design adopts relative counting method. Before the operation, the number of pulses at the corresponding floor height is measured by the self-learning method, and for the 17 elevator, it is stored in the 16 storage unit D0 1-D 16 respectively.
The floor counter CNTl0 is a two-way counter. When you reach the floor counting point of each floor, count up or down 1 according to the running direction.
During operation, the accumulated value of the high-speed counter is compared with the number of pulses corresponding to the floor counting point in real time, and when they are equal, the floor counting signal is sent out, with the uplink increasing by 1 and the downlink decreasing by 1. In order to prevent the counter from counting repeatedly during the high level of the counting pulse, the floor counter is triggered by the upper edge of the floor counting signal.
4.2 Fast speed change
When the value of the high-speed counter is equal to the number of pulses corresponding to the fast speed change point, if the elevator runs fast and there is a floor selection signal, the fast speed change signal is sent. If the elevator is running at medium speed or fast speed but there is no floor selection signal, the speed change signal will not be sent. The judgment method of medium-speed change is similar to that of rapid change, so I won't repeat it here.
4.3 Gate area signal
When the value of the high-speed counter CNT47 is within the range of the number of pulses corresponding to the gate, the gate signal is transmitted. The judgment method of flat signal is similar to that of regional signal, and will not be described in detail.
4.4 Pulse signal fault detection
In this system, the accurate acquisition and transmission of pulse signal is particularly important. In order to detect the faults of rotary encoder and pulse transmission circuit, pulse signal and leakage pulse detection circuits are designed to ensure the normal operation of the system through real-time detection. In order to eliminate the accumulated error of pulse counting, a reset switch is set in the base station and connected to the reset terminal 000 1 of the PLC high-speed counter CNT47.
5 conclusion
Based on the principle of centralized electrical control, the system described in this paper adopts pulse counting method, uses pulse encoder to replace the original position detection device in the hoistway to realize displacement control, and uses software to replace some hardware functions, which not only reduces the system cost, but also improves the reliability and safety of the system, and realizes the full digital control of the elevator.
On the basis of laboratory debugging, two 17-floor elevators were reformed on the spot by the above method. The test of related parts and the actual operation in the past year show that the system is reliable, comfortable to ride, the failure rate is greatly reduced, the leveling accuracy is within 5mm, and good operation results are achieved. refer to